Josephine Healey, who has had little contact with Moat for 18 years, said the self-confessed “maniac” being hunted by police in Northumberland was a different person in “every last detail” to the son she remembered.

Referring to school photographs showing a contented-looking child with a toothy smile, and contrasting them with the hulking bodybuilder now on the loose, she said: “This man does not look like my son.

“I feel like he hasn’t been my son since he was 19 years old. He now has a totally different character, attitude and manner. Now when I see him I don’t recognise him at all. He would be better off dead. If I was to make an appeal I would say he would be better dead.”

Mrs Healey, 63, spoke as police disclosed that they had found Moat’s hideout at Wagtail Farm, Rothbury, close to where the Lexus car he had been using was discovered on Tuesday.

Inside a tent Moat had been using, officers found an eight-page letter addressed to his ex-girlfriend, Samantha Stobbart, one of the three people he shot over the weekend, in which he repeated threats to kill police officers.

He “declared war” on Northumbria Police in a 49-page note handed to police via a friend early on Monday.

Det Chief Supt Neil Adamson, who is leading the manhunt, said he believed that Moat, 37, was still in the Rothbury area, and offered a £10,000 reward to anyone who could help secure his arrest.

Moat’s mother, from Fenham, Newcastle upon Tyne, said her son had chronic asthma as a child and did not have many friends.

“He was like all little boys,” she said. “We used to find him with pockets full of spiders.”

After leaving school at 16 he began karate lessons and “would always be sitting around in his white karate outfit”.

Then, after Mrs Healey married her current husband, Brian, Moat and his elder brother Angus, 39, fell out with their mother and she did not see Moat for 10 years.

Mrs Healey said one of the last times she saw Moat was in 2007 when he turned up on her doorstep and threatened her. “It was like he was not my real son. He did not want anything to do with me. He put his two fingers pointing to me like a gun.”

Scores of armed officers, including snipers, from eight police forces are now searching for Moat, who wounded Miss Stobbart, 22, early Saturday and shot dead her boyfriend, Chris Brown, 29, before shooting Pc David Rathband, 42.

On Wednesday evening, armed police were seen escorting an associate of Moat's - someone not previously involved in the case - into the woods at Wagtail Farm to assist their investigation into the hideout used by Moat.

In the new letter, Moat tries to justify Mr Brown’s murder, saying he was shot because Miss Stobbart said he was a policeman. In fact, Mr Brown was a karate instructor, but Miss Stobbart had lied to Moat in the hope that he would stay away when he was released from prison last Thursday.

As the search for Moat headed toward its sixth day, Mr Adamson said the police were making significant progress. “I’m confident we will apprehend Mr Moat very, very soon,” he said.

However, he admitted it was possible Moat had slipped through the police cordon at Rothbury.

Several people — including Marissa Ree, the mother of two of his three children – remained under police protection amid fears Moat could target them.